It has been desirable in the art to develop economical, marketable by-products of waste glass which can be manufactured by efficient and cost effective processes. One such by-product is "foamed glass" which is well known in the art. See, e.g., U.S. Pat. No. 3,874,861 of Kurz, the teachings of which are incorporated specifically herein by reference. One of the many uses for foamed glass is in the stone-washed garment industry, wherein a foamed glass article can be used in place of natural pumice to obtain a very desirable "stone-washed" look for denim, silk, and other textile products.
The known art of foaming glass teaches a variety of methods and compounds for improving foamed glass and related products. In U.S. Pat. No. 4,207,114 (Schuster), for example, a foamed glass product and method are disclosed having fire-resistant and fluid permeability properties achieved through controlled foaming. U.S. Pat. No. 3,207,588 (Slayter) teaches a glass foam having improved insulating properties by using finely meshed glass to produce finer and more uniform foamed glass cells, and a more lightweight foamed glass. Other art discloses alternate methods for foaming glass, primarily for use in the construction industry as, for example, in U.S. Pat. Nos. 2,987,441 (Minnick), 2,691,248 (Ford), 4,347,326 (Iwami) and 4,826,788 (Dennert). Other art teaches preferred apparatuses for manufacturing foamed glass, such as in U.S. Pat. Nos. 5,049,333 (Wolfe), 4,038,063 (Williams) and 4,124,365 (Williams).
The present invention, however, is not directed toward the construction or insulating industries but, rather, the garment stone-washing industry. The ability of foamed glass used in stone-washing to insulate, for example, is not relevant. Other art has focused on stone-washing garments. U.S. Pat. No. 4,933,306 to Pietsch teaches an improved artificial pumice stone for use in the garment industry. The focus of Pietsch is on decreasing abrasivity of the articial pumice and increasing mechanical strength to enhance the use of cellular glass in the garment industry. Similarly, U.S. Patents to Oat, U.S. Pat. Nos. 5,266,087, 5,326,383 and 5,359,745 disclose improvements in the prior art related to foamed glass in the garment industry as a function of improving product attrition rates and abrasiveness. The focus of the present invention is on neutralizing pH of foamed glass to diminish or prevent interference with enzyme activity in the garment stone washing process, not on affecting foamed glass product abrasiveness. U.S. Pat. No. 4,308,065 (Walls-Muycelo) does address pH levels, but in the construction industry, not the foamed glass industry. U.S. Pat. No. 4,308,065 also acknowledges that, conventionally, highly alkaline products are used in the expanded aggregates industry. The chemical processes disclosed and components used in U.S. Pat. No. 4,308,065 are completely different than those of the present invention.
Generally, foamed glass is made by finely pulverizing glass particles and thoroughly mixing with the pulverized glass particles an amount of foaming agent, binder and water to produce a glass particle mixture. The glass particle mixture is formed into a glass article of the desired size and shape and heated for a time to a temperature above the softening point of the glass to cause the glass particles to fuse to one another and substantially all the remaining foaming agent to emit foaming gas emissions, thereby causing cellulation or foaming. The heated foamed glass article then is cooled to produce the finished foamed glass article.
A commonly used foaming agent of choice in prior art is calcium carbonate (CaCO.sub.3). A glass and CaCO.sub.3 mixture having a content of about 0.01% to 28% CaCO.sub.3 has been found previously to produce a foamed glass article satisfactory for the stone washing of garments, except that a foamed glass article formed with an excess of 5% by weight CaCO.sub.3 tends to have a high pH, that is, it is alkaline or basic. It has been determined that a high pH foamed glass article is undesirable for stone-washing garments. One reason for this is that high pH foamed glass interferes with enzymes now used more and more frequently in garment stone-washing. Therefore, the alkaline foamed glass articles found in prior art generally are not suitable where certain desirable enzymatic additives are used in the stone washing process. As the use of pH sensitive enzymes is increasing in the stone washing industry, there thus exists a need in the art for a substantially neutral pH foamed glass article, within the pH range of 7.0 to 8.4.
The residue produced by the wearing away of foamed glass stones is of substantially higher quality than the sludge produced in connection with natural pumice. Pumice sludge is useless and must be disposed of in a landfill at substantial cost to the user. Foamed glass residue, on the other hand, once separated from the garment processing waste stream, is virtually 100% glass, and a substantial amount of this glass can be re-used in the manufacture of other foamed glass articles, and for other foamed glass uses, such as in the construction industry.
A foamed glass article described herein can be made almost totally from mixed color waste glass cullet, for which in most parts of the country there is a limited market. The methods disclosed and claimed herein make a major contribution towards recycling efforts and to the environmental improvement of the nation. The use of a foamed glass article of the present invention will substantially completely eliminate the need of strip-mining of natural pumice deposits worldwide. It also appears that it may be possible to produce a foamed glass article at less expense than the cost of producing pumice stones from natural pumice, which includes mining, crushing, screening, and very large transportation costs. This may result in economies to the stone-washing companies and lower prices for consumers.
One object of the present invention is to provide an improved foamed glass process and product which is substantially pH neutral for use in the garment stone-washing industry.
Another object of the present invention therefore is to provide an improved foamed glass process and product for garment industry uses which is substantially pH neutral and has a low attrition rate.
Another object of the present invention is to provide an inexpensive, environmentally sound, efficient process for manufacturing substantially pH neutral foamed glass.